1. Field of the Invention
The present invention generally relates to a full-color image forming apparatus, for example, a full-color copier, a full-color facsimile and a full-color printer, capable of making a full-color developer image by using a revolving type developing device for developing latent images with a plurality of monochrome developers. More particularly, the present invention relates to an optical communicating device for optically communicating a signal between the revolving type developing device and a body of an image forming apparatus.
2. Description of the Related Art
In a full-color image forming apparatus, a revolving type developing device is generally used.
Such a revolving type developing device generally includes four monochrome developing rooms for developing a latent image with monochrome developers, for example, yellow developer, magenta developer, cyan developer and black developer. The developing rooms are disposed around an axis of the revolving type developing device and each room separately stores one of the monochrome developers therein. A latent image is repeatedly formed on an image carrier to be separately developed by each of the plurality of monochrome developers and then separately developed by a corresponding one of the monochrome developers in a predetermined order and finally superimposed on a copy sheet, thereby obtaining a full-color developer image.
In such a conventional developing device, since a density of each of the monochrome developers has to be kept within a predetermined range to obtain a full-color copy of good quality, a density sensor is generally provided in the developing rooms and is generally utilized to sense density. Such a density sensor generates a signal indicative of density and the signal is sent to a controller for controlling a developer supplying device for supplying new monochrome developer to a corresponding developing room to keep a density of the developer within a predetermined range.
Thus, the density signal is generally sent from the revolving type developing device to a controller disposed in a body of the image forming apparatus. As shown in Japanese Laid Open Patent Application Number 08-69144, to send a density signal from a revolving type developing device to a body of an image forming apparatus, a plurality of optical beam generating members are provided on a side plate of a revolving type developing drum. Each member communicates density information from a sensor provided in a corresponding developer storing room of the drum to the body of the image forming apparatus. Each member irradiates a light beam indicating a density sensed by the corresponding density sensor disposed in the corresponding developer storing room. The plurality of optical beam generating members are generally disposed on a circumference circle on a side plate and around an axis of rotation of the revolving type developing device with a predetermined interval therebetween (e.g., at 90.degree. intervals).
To receive light beams generated by the optical beam generating members, a photoreceptor is disposed at a portion of a body of the image forming apparatus which faces one of the optical beam generating members, when the revolving type developing device is rotated to a predetermined position. The photoreceptor is capable of receiving a light beam irradiated from one of the optical beam generating members, each time the revolving type developing device rotates through an angle of 90.degree..
A density signal received by the photoreceptor is input to a controller for controlling a monochrome developer supplying device for supplying new monochrome developer into a corresponding developing room to maintain the density of the monochrome developer stored therein within a predetermined range. In this way, the density signal is optically communicated from the revolving type developing device to the body of the image forming apparatus.
However, such a conventional optical sensing device is excessively costly, since it requires the use of a plurality of optical beam generating members, a complex control system for controlling the sensors to start sensing density and difficulties in providing a precise arrangement of the optical beam generating members on the side plate of the revolving type developing device.
As shown in Japanese Laid Open Patent Application Number 08-267627, an optical signal is communicated from a revolving type developing device to a body of an image forming apparatus. In this device, a light emitting diode (LED) for generating a light beam having density information relating to one of the monochrome developers is disposed in an opening of a shaft which extends from a side of the device and on the axis of rotation of the revolving type developing device.
To receive such a light beam, a photo-transistor is disposed at a portion of a body of the image forming apparatus so that the photo-transistor faces the LED. Density information is thus optically communicated from the LED to the image forming apparatus, when the LED irradiates a light beam. However, such an arrangement does not allow for mutual communication of optical information between the revolving type developing device and the body of the apparatus. In addition, the shaft in this unit extends a distance from the end of the revolving type developing device, thus making the size of the unit relatively large.
The above described apparatuses are not particularly suited for use with an optical communicating system for mutually communicating information between the image forming apparatus and the revolving type developing device. As shown in FIG. 1, an optical communicating system for mutually communicating optical information includes a first unit plate mounting a light beam generating member 501a for generating a light beam and a photoreceptor 501b for receiving a light beam. A second unit plate mounts a light beam generating member 502a for generating a light beam toward the photoreceptor 501b of the first unit plate and a photoreceptor 502b for receiving a light beam irradiated from the light beam generating member 501a of the first unit plate.
The reason that such an optical communicating system cannot be readily used in the above-described apparatuses is that the optical communicating system cannot be disposed on a side plate 504 on a center line extending from the axis of the revolving type developing device. For example, as shown in FIG. 1b, if the first unit plate mounting the light beam generating member 501a and the photoreceptor 501b is disposed on the side plate 504 on the center line of the axis of the revolving type developing device, optical communication can only be performed when the unit plates are aligned at predetermined positions. That is, although the light beam generating member 501a inherently has a predetermined diffusion angle, the light beam generated thereby is not capable of covering a corresponding photoreceptor 502b mounted on the second unit plate which is attached to the body 506 of the apparatus when the revolving type developing device rotates, until the first unit plate has rotated to the position as shown in FIG. 1a.
Further, as shown in FIG. 1c, if both units are disposed sufficiently far from each other to enable the light beams generated by the light beam generating members to cover the corresponding photoreceptors, an image forming device necessarily becomes too large.